2016-10-09 18:31:45

Prelude

Today's Topics

  • Exam 2 on Friday
  • Extra point for mistake on Quiz 2, Question 9
  • Homeostasis

What is homeostasis?

Homeostatic mechanisms depend on negative feedback

Domains

  • Temperature
  • Food intake/body mass

Temperature regulation

Temperature regulation

  • Too cold: ice crystals disrupt cell membranes
  • Too hot: molecular disruption

Varieties of thermal regulation

Regulation Type Endothermic Ectothermic
Homeothermic Birds, mammals, some large fish Tropical reptiles
Poikilothermic Some birds, mammals Most fish, amphibians, invertebrates

Ectothermy vs. endothermy

  • Ectothermy
    • Behavioral regulation >> metabolic regulation
    • Older (evolutionarily-speaking), more species

Ectothermy vs. endothermy

  • Endothermy
    • Metabolic regulation > behavioral
    • Newer and fewer species

Benefits/costs of endothermy

  • Benefits
    • Sustained muscular activity?
    • Occupy more, more diverse ecological niches
    • Sociality, behavioral complexity?
  • Costs
    • Metabolism
    • Food seeking
    • Body size

Big bodies conserve heat; little ones lose it

  • Heat produced ~ volume or mass (~ length^3)
  • Heat loss ~ surface area (~ length^2)
  • Big animals have >> volume/surface area ratio

Bergman's rule

Inputs/outputs

  • Inputs
    • Body temperature
    • External temperature
    • Brain (hypothalamus)
  • Outputs
    • Autonomic/endocrine
    • Somatic/behavioral

Control mechanisms

  • No single controller.
  • Responses to heating ≠ responses to cooling

Response to heating

Response Type Response to Heating Response to Cooling
Autonomic/endocrine Vasodilation Piloerection
Sweating Increased fat metab
Somatic/behavioral Panting Shivering
Heat avoidance Heat seeking
Huddling

Control mechanisms

  • Hypothalamus
    • Preoptic area (POA)
      • Autonomic response
    • Lateral hypothalamus
      • Behavioral responses
  • Brain stem, spinal cord

Big brains, big appetites

Big brains/complex behavior related

Food seeking

  • Grazing vs. gathering vs. hunting
  • Quality vs. quantity
  • Time/energy to find & consume

Just keeping the lights on…

  • 60-70% daily calories -> basal metabolism
  • 20% behavior
  • 10% thermoregulation & digestion

Why dieting is hard, often ineffective

Next time…

  • Review for Exam 2